Regulation of the output power of an amplifier stage is subject to predefined requirements, particularly in data transmission systems. Thus, e.g., in the UMTS standard (Universal Mobile Telecommunication System), a modification of the output power of a transmitter in a mobile terminal device is prescribed [1]. This is required, because a poor or incorrect setting of the output power would influence other connections over the same channel or reduce their transmission quality. In a communication system, a base station therefore regularly, e.g. at a rate of 1.5 kHz, transmits commands that specify corrections for the output power values to the mobile terminal device. These corrections may lie in orders of magnitude of −3 dB to +3 dB. It is required that a mobile terminal device follows these commands and maintains predefined tolerances so as not to affect its own transmission quality and the transmission quality of other mobile terminal devices transmitting on a same channel. In comparison, the entire dynamic range of a UMTS data transmission system is more than 70 dB.
It is known for an “open-loop” approach to be adopted in the mobile terminal device. The output power in the mobile terminal device is not monitored directly, but merely modifications to the output power are carried out according to correction signals sent by the base station.
A “closed-loop” approach may be adopted due to more stringent requirements from network operators in terms of the equivalent radiated output power of mobile terminal devices. In the closed-loop approach, a feedback loop is provided within the mobile terminal device, by means of which the output power of the amplifier stage is monitored. The output power is regulated according to a output power measured in the mobile terminal device. E.g., a closed-loop approach may be applied in order to guarantee the quality of the mobile terminal devices in the event of a mismatching of antennas. At the same time, it is ensured that the maximum output power specified in the standard is not exceeded.